You need a specific formula to prove the project's financial worth and calculate its exact payback period 1]. To calculate annual ROI, use this formula: (Annual kWh Generation × Your Electricity Rate) ÷ (Total System Cost - Incentives) × 100. In today's renewable energy boom, photovoltaic brackets. How to calculate the profit o onnected photovoltaic(PV) energy systems throughout the world. Select the "Grid-tied&quo ; menu to get the. Caution: Photovoltaic system performance predictions calculated by PVWatts ® include many inherent assumptions and uncertainties and do not reflect variations between PV technologies nor site-specific characteristics except as represented by PVWatts ® inputs. Standard mounts range from $100 to $400 per set, while advanced systems may exceed $1,000. The results are presented graphically, divided into four sub-categories: Results, effect of leverage, effect of irradiation and panel price, effect of inflation. determines the number of modules to be purchased.